Understanding microbial contamination

I just did a boat service for someone on his engine and I told to him : "You've got a bit of diesel bug in the tank". But what is this really ? When you are told you have got microbial contamination. There are 120 difference types micro-organisms growing in diesel : bacteria, yeasts, fungus. That are all growing in diesel, they live in oxygen and water that you've got into your diesel, and they eat the carbon out of the diesel. What does that mean to you ? It means a big black mess is growing in your tank. And as you go along, it will break up, it will block the filters and the engine will stop. So we've got to get rid of it.